Device for power line communication, method for transmitting signals, and method for receiving signals

ABSTRACT

A device for power line communication is provided, including a transmitter adapted to transmit signals on at least two of a plurality of power line transmission paths of a power line network; a sensor adapted to determine one or a plurality of reflection parameters of one of the plurality of power line transmission paths; and a transmission impedance matching unit adapted to match the output impedance of at least two output ports of the device which each couple to one of the plurality of transmission paths to the impedance of the at least two of the power line transmission paths based on the one or the plurality of reflection parameters. Further, a device including a corresponding reception impedance matching unit is provided and corresponding methods for transmitting and receiving signals.

This application is a continuation of application Ser. No. 14/431,007,filed on Mar. 25, 2015, which is a National Stage Application ofInternational Application No. PCT/EP2013/002867, filed on Sep. 24, 2013,which claims the benefit of priority from European Application No.12007050.3, filed Oct. 11, 2012, the entire contents of each of theabove applications are incorporated herein by reference.

BACKGROUND

Field of the Disclosure

The present disclosure relates to a device for power line communication,a method for transmitting signals and a method for receiving signals.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Current power line communication modems (PLC modems) are based on singleinput-single output (SISO) schemes. In a single input-single outputscheme the signals are fed into a pair of dedicated wires (for instancebetween the phase or live (P or L) wire and the neutral (N) wire) of apower line network in a building. However, multiple input-multipleoutput (MIMO) schemes are currently investigated in order to improvee.g. data rate, coverage, robustness against disturbances, utilizing thediversity of the MIMO channel and consideration of electromagneticinterference (EMI) regulations. In MIMO schemes signals are fed intoand/or received from at least two combinations of different wires bydifferent input and/or output ports, e.g. between phase and neutral,phase and protective earth (PE), and neutral and protective earth (PE)in a three wire power line network. It is also possible to receivesignals from a common mode (CM) signal received between any of the wiresto ground.

Power line networks may exhibit strong variations in input impedances atindividual transmission frequencies, at different locations of theoutlets in the building and due to changing network topology (e.g. whena light switch is toggled by a user). This may have negative impact whenfeeding and/or receiving power line signals into and/or from power linenetworks.

SUMMARY

A device for power line communication is provided including atransmitter adapted to transmit signals on at least two of a pluralityof power line transmission paths of a power line network; a sensoradapted to determine one or plurality of reflection parameters of one ofthe plurality of power line transmission paths; and a transmissionimpedance matching unit adapted to match the output impedance of atleast two output ports of the device which each couple to one of theplurality of transmission paths to the impedance of the at least two ofthe power line transmission paths based on the one or the plurality ofreflection parameters. The reflection parameters might be individuallyadapted at each frequency. There might be one or a plurality ofreflections parameters for each input or output port.

Further, a device for power line communication is provided, including areceiver adapted to receive signals on at least two of a plurality ofpower line transmission paths of a power line network; a sensor adaptedto determine one or a plurality of reflection parameters of one of theplurality of power line transmission paths; and a reception impedancematching unit adapted to match the input impedance of at least two inputports of the device which each couple to one of the plurality oftransmission paths to the impedance of the at least two of the powerline transmission paths based on the one or the plurality of reflectionparameters. The impedance matching unit might adapt the impedancematching individually at each frequency of might select the identicaltermination to all frequencies.

Further, a method for transmitting signals from a device via a pluralityof transmission paths of a power line network is provided, includingdetermining one or a plurality of reflection parameters of one of theplurality of power line transmission paths; and matching an outputimpedance of at least two output ports which each couple to one of theplurality of power line transmission paths to the impedance of at leasttwo of the power line transmission paths based on the one or theplurality of reflection parameters.

Further, a method for receiving signals in a device via a plurality ofreception paths of a power line network is provided includingdetermining one or plurality of reflection parameters of one of theplurality of power line reception paths; matching an output impedance ofat least two input ports which each couple to one of the plurality oftransmission paths to the impedance of at least two of the power linereception paths based on the one or the plurality of reflectionparameters.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings. Theelements of the drawings are not necessarily to scale relative to eachother.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic block diagram of a device according to anembodiment of the invention;

FIG. 2 is a schematic block diagram of a device according to a furtherembodiment of the invention;

FIG. 3 is a schematic block diagram of a device according to a furtherembodiment of the invention;

FIG. 4 is a schematic diagram illustrating possibilities to feed signalsinto a 3 wire power line system and to receive signals from the 3 wirepower line system;

FIG. 5 illustrates a measured attenuation versus frequency for differentfeeding and reception possibilities;

FIG. 6 illustrates a measured reflection parameter S11 versus frequencyfor a star-style coupler at an outlet;

FIG. 7a illustrates a cumulative distribution function of the magnitudeof the reflection parameter S11 from a T-style coupler;

FIG. 7b illustrates a cumulative distribution function (CDF) of themagnitude of the reflection parameter S11 from a Delta-coupler;

FIG. 7c illustrates a cumulative distribution function (CDF) of themagnitude of the reflection parameter S11 from a Star-style coupler;

FIG. 8 illustrates the impedance in Ohm versus frequency at ports D1 toD3 of a delta-type coupler of an outlet;

FIG. 9 shows a schematic flow diagram of a method according to anembodiment of the invention; and

FIG. 10 illustrates a schematic flow diagram of a method according to afurther embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, in FIG. 1a device 100 for power line communication according to an embodiment ofthe invention is depicted.

The device 100 includes a transmitter 102 adapted to transmit signals onat least two of a plurality of transmission paths 104, 106 of a powerline network 110. The plurality of transmission paths might include afirst transmission path as a differential mode feeding between phase (P)or live (L) wire and neutral wire (N), a second transmission path as adifferential mode feeding between the phase (P) or live (L) wire and aprotective earth wire (PE), a third transmission path as a differentialmode feeding between the neutral wire (N) and the protective earth (PE)wire. It might also be possible that a transmission path might be builtby feeding a differential mode between a middle point of L and N towardsprotective earth.

The transmitter 102 transmits the signals via output ports 180, 190,which each couple with one of the transmission paths 104, 106 used,respectively.

The transmitter might include a power line signal processing unit 150and an analog-to-digital-converter, digital-to-analog-converter 160.

A sensor 120 is further included in the device 100. The sensor 120 isadapted to determine one or a plurality (e.g. a set) of reflectionparameters, also called reflection coefficients or scattering parameters(S11), of one of the plurality of power line transmission paths 104,106, in the depicted example the reflection parameter for the firsttransmission path 104. The reflection parameter is also referred to as“S11-parameter”. Sensing the reflection parameter might in oneembodiment be performed by transmitting a signal into the power linesand measuring the reflected return signal. It is known by a personskilled in the art to use for this a signal source, a reflection bridgeand a signal detector.

Based on the determined S11- or reflection parameter a transmissionimpedance matching unit 130 in the device 100 is adapted to match theoutput impedance of the at least two output ports 180, 190 of the deviceto the impedance of the at least two of the power line transmissionpaths 104, 106. Matching the impedance is done by adjusting theimpedance of the impedance matching unit 130 to the conjugate compleximpedance of the network (or the individual transmission paths,respectively). The transmission impedance matching unit 130 might bebased on programmable analog arrays.

The impedance matching unit 130 might adapt the impedance matchingindividually at each frequency of might select the identical terminationto all frequencies.

Since the impedance is matched identically for at least two output portsand two transmission paths based on a single measurement of thereflection parameter, impedance matching is performed very efficiently.

The power line signal processing unit 150 might optionally include anamplifier 170 that amplifies the power of a signal with an amplificationfactor prior to transmission, wherein the amplification factor is basedon the reflection factor determined by the sensor 120. This might beused to perform a power boost when signal energy is reflected at thefeeding outlet. The amplifier might also be located on the analog sideone the right hand side of theanalog-digital-converter/digital-to-analog converter 160 in FIG. 1. Ingeneral, for regulatory purposes only the energy already fed to themains grid on the test setup is measured for verifying the transmissionpower. Energy that is reflected at the outlet will not be fed into thegrid. This lost energy might be boosted by the PLC modem beforetransmitting it to the mains. Here the sensing of the reflection datamight be done on one path only and applied to the power boost of all orsome of the MIMO paths.

In FIG. 2 a device 200 according to a further embodiment of theinvention is depicted. The device 200 includes a receiver 202 adapted toreceive signals on at least two of a plurality of reception paths 204,206, 207 of the power line network 110. The reception paths mightinclude a first reception path as a differential path between a phase(P) or live (L) wire and a neutral wire (N), a second reception path asa differential path between phase (P) or live (L) wire and protectiveearth wire (PE), a third reception path as a differential path betweenneutral wire (N) and protective earth (PE) wire. A reception path mightalso be a single ended path, a common mode path or a differential pathbetween the middle point of L and N wire and protective earth.

The receiver might include a power line signal processing unit 250 andan analog-to-digital-converter 260.

A sensor 220 is further included in the device 200. The sensor 220 isadapted to determine reflection parameters of one of the plurality ofpower line reception paths 204, 206, 207 in the depicted example thereflection parameter for the first reception path 204.

Based on the determined S11- or reflection parameter a receptionimpedance matching unit 230 in the device 200 is adapted to match theinput impedance of at least two input ports 284, 285, 286 of the device200 to the impedance of the at least two of the power line receptionpaths 204, 206, 207. The reception impedance matching unit 230 might inone embodiment be based on programmable analog arrays, which mightinclude multiple capacitive of inductive components. Alternatively, theymight be implemented by switchably arranged discrete hardwarecomponents. The impedance matching might be done individually for eachfrequency.

Since the impedance is matched identically for at least two input portsand at least two reception paths based on a single measurement of thereflection parameter, impedance matching is performed very effectively.

The sensor 220 might be further adapted to measure the reflectionparameters of a common mode reception path 240, so that the receptionimpedance matching unit 230 is enabled to match the input impedance of acommon mode input port 290 to the common mode reception path 240 aswell.

In FIG. 3 a device 300 for power line communication, e.g. a power linecommunication modem (PLC modem) according to a further embodiment isdepicted. This device 300 includes transmitter and receiverfunctionality, which is exemplarily realized and depicted by a commonPLC signal processing unit 350 and the analog-to-digital-converter 260for the receiver functionality and a digital-to-analog-converter 355 forthe transmitter functionality.

A sensor 320 is included in the device 300, which is adapted todetermine the reflection parameters of one of the transmission paths104, 106, and is further adapted to determine the reflection parametersof one of the reception paths 204, 206, 207 which are used for receivingdifferential mode signals, and is, for instance, further adapted todetermine the reflection parameters of the common mode reception path240. In other embodiments, the sensor 320 is only adapted to measure oneof the reflection parameters mentioned above.

Further to the reception impedance matching unit 230 as described withregard to FIG. 2, the device 300 may include a transmission impedancematching unit 335. The sensor 320 provides the determined reflectionparameters for the one transmission path to the transmission impedancematching unit 335 and the reflection factors for the one reception pathand for the common mode reception path 240 to the reception impedancematching unit 230. Based on the determined reflection parameters, thetransmission impedance matching unit 335 and the reception impedancematching unit 230 adapt the input and the output impedances of the inputports 180, 190 and the output ports 284, 286, 287 and 290 of the device300 to the impedance of the transmission paths 104, 106 and to thereception paths 204, 206, 207, 240.

Since the impedance is matched identically for at least two transmissionpaths based on a single measurement of the reflection parameters, andthe impedance is matched identically for at least two reception paths,impedance matching is performed very efficiently.

FIG. 4 depicts different kinds of feeding and receiving styles for MIMOpower line communication. The dashed lines in the middle of FIG. 4represent individual wires of a mains grid. Components that are used forsafety or blocking the AC voltage on the mains grid are not depicted inFIG. 4. On the left hand side two different known feeding couplers(Delta-style coupler 400 and T-style coupler 402) are shown. The righthand side shows three different known receiving couplers: Star-stylecoupler 405, Delta-style coupler 410 and T-style coupler 412.

To avoid the injection of Common Mode (CM) signals, feeding PLC signalsshould be done using Delta-style coupler 400 (top left side in FIG. 4)or T-style coupler 402 (lower left side in FIG. 4) couplers. Thesymmetrical implementation of the Delta-style coupler 400 and theT-style coupler 402 guarantees that no CM signals are generated at thepoint of signal injection.

The Delta-style coupler 400 or also called transversal coupler consistsof three baluns arranged in a triangle between live, neutral andprotective earth. The sum of the three voltages injected is equal tozero (as proven by Kirchhoff's law). Hence, only two of the threesignals are independent of each other.

FIG. 7 shows statistical data on the properties of multiple PLCchannels.

These data are recorded where all three baluns were present andterminated by 50Ω on the measurements instruments site (at ports D1, D2and D3). Terminating the ports provides most reproducible results andavoids additional signal reflections caused by connecting measurementequipment.

When terminating the three wire system, the impedance of each wire pairis present three times in parallel. A PLC modem implementation mightterminate two or three of the three wires with e.g. a low impedance fortransmissions and a high impedance when receiving signals. All balunsmight be of the same type (for instance, Guanella transformers 1:4 witha very low loss).

The T-style coupler 402 feeds a differential mode signal between liveand neutral contact plus a second signal between the middle point oflive-neutral to the protective earth. The second signal is a quasicommon mode signal between live-neutral and the earth wire. Again, thetwo T-ports are terminated to minimize reflections at the coupler.

Receiving the PLC signals (depicted at the right side in FIG. 4) is alsopossible using the star-style or longitudinal coupler 405. The threewires are connected in a star topology to the center point. Here,Kirchhoff's law also forces the sum of all currents arriving at thecenter point to be zero. Hence, only two of the three signals areindependent. However, due to parasitic component in a coupler thereception of the signals at the third port additionally improves thethroughput capacities of MIMO PLC. Furthermore the star-style coupler405 allows the reception of common mode signals which enables a forthreceive path. The CM transformer is magnetically coupled (Faraday type).

A Delta-style coupler 410 and a T-style coupler 412 might also be usedfor signal reception. Feeding signals using the Star-style coupler mightcause injecting CM signals resulting in radiations and interferenceproblems to radio applications.

Safety components in the couplers to protect the operator and thesensitive measurement equipment (50 Hz level, surge protection) aredocumented in [ETSI TR 101 562-1]. The ETSI TR also documents thecalibration data of the couplers.

FIG. 5 depicts of the attenuation as collected by individual frequencysweeps of all MIMO channels between two outlets. There are 12 sweeps intotal transmitted at the ports D1, D2 and D3, respectively, of theDelta-style coupler 400 and received at the ports S1, S2, S3 and the CMport S4, respectively, of the Star-style coupler 405.

Attenuation or channel measurements of individual MIMO paths provide asignificant variance in between the individual paths. At mostfrequencies the difference between the maximally and the minimallyattenuated paths is more than factor 100.

FIG. 6 presents a sweep recording the reflection parameter at theStar-style coupler 405. The three single ended ports S1, S2 and S3 showabove 10 MHz very similar reflection characteristics. The common mode(CM) sweep (S4) provides less variance over the frequency. The commonmode signal is the voltage between the sum of the three Star-stylesignals and ground.

FIGS. 7a, 7b and 7c show an overview of the probability of measuring areflection parameter by depicting the cumulative probability of S11 fora T-style coupler 402, 412 (FIG. 7a ), a Delta-style coupler 400, 410(FIG. 7b ) and a Star-style coupler 405 (FIG. 7c ). FIG. 7 shows veryhigh reflection coefficients. This results in weak impedance matchingconditions of the power line network (indoor power line network) wherethe measurements have been taken. If the S11 parameter is less (morenegative) than −6 dB, more than half of the feed signals are reflectedback to the coupler and the connected outlet. This is the case for morethan 60% of all S11 measurements conducted using delta ports D1, D2, orD3 or the T-feeding port T1. Thus, it is clear that enhanced impedancematching might improve the throughput rates of PLC modems considerably.

As can be derived from FIG. 7, the absolute scattering parameter |S11|of the CM port and the single ended lines S1, S2 and S3 of theStar-style coupler 405 and the differential mode T2 of the T-stylecoupler has higher values than the absolute scattering parameter |S11|of the differential modes of the Delta-style coupler and thedifferential mode T1 of the T-style coupler.

The impedances of the delta ports D1, D2 and D3 at an exemplary outletare shown versus frequency in FIG. 8. It can be observed that thevariance of the impedance values in-between the individual ports issmall. This phenomenon was also found at the single ended Star-ports ofFIG. 4, see the measurement results shown in FIG. 6. Hence, for matchingthe impedance of a MIMO PLC coupler to the mains, the MIMO paths can bematched identically (i.e. using one or more reflection parametersmeasured for only one of the MIMO paths).

When PLC signal feeding is performed with the Delta-style coupler 400and receiving is done by the Star-style coupler 405, the ports D1, D2and D3 of the Delta-style coupler 400 might be terminated identicallyand the ports S1, S2 and S3 of the Star-style coupler 405 might also beterminated identically. The group of the D-port's termination and thegroup of the S-port's termination might be matched individually.

PLC modems might also perform a power boost when signal energy isreflected at the feeding outlet. In general, for regulatory purposesonly the energy already fed to the mains grid on the test setup ismeasured for verifying the transmission power. Energy that is reflectedat the outlet will not be fed into the grid. This lost energy might beboosted by the PLC modem before transmitting it to the mains. Here,again, the sensing of the reflection data might be done on one MIMO pathonly and applied to the power boost of further MIMO PLC paths.

In FIG. 9 a schematic flow diagram of a method for transmitting signalsfrom a device for power line communication via a plurality oftransmission paths of a power line network is depicted. In S900reflection parameters are determined for one of the plurality of powerline transmission paths, which is used in S902 to match an outputimpedance of at least two output ports of the device to at least two ofthe power line transmission paths.

In FIG. 10 a schematic flow diagram of a method for receiving signals ina device for power line communication via a plurality of reception pathsof a power line network is depicted. In S1000 reflection parameters ofone of the reception paths is determined, which is used in S1002 tomatch an input impedance of at least two input ports of the device to atleast two of the power line reception paths.

With the proposed devices and methods it is possible to match the inputand output impedances to a plurality of transmission and reception pathseffectively, since only the reflection parameter of one of therespective paths has to be measured and identical impedance matches canbe used for a plurality of paths.

Obviously, numerous modifications and variations of the presentdisclosure are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The invention claimed is:
 1. A device for power line communication, thedevice comprising: a multiple-input-multiple-output (MIMO) transmitterconfigured to concurrently transmit signals via a first output portcoupled to a first power line transmission path and a second output portcoupled to a second power line transmission path, the first and secondpower line transmission paths included in a plurality of power linetransmission paths of a power line network; and a transmission impedancematching circuit configured to identically match, based on at least onereflection parameter of at least one of the first and second power linetransmission paths, a first output impedance of the first output port toa first impedance of the first power line transmission path and a secondoutput impedance of the second output port to a second impedance of thesecond power line transmission path, wherein the at least one reflectionparameter is predetermined.
 2. The device according to claim 1, furthercomprising: a MIMO receiver configured to concurrently receive signalsvia a first input port coupled to the first power line transmission pathand a second input port coupled to the second power line transmissionpath; and a reception impedance matching circuit configured to match,based on the at least one reflection parameter, a first input impedanceof the first input port to the first impedance of the first power linetransmission path and a second input impedance of the second input portto the second impedance of the second power line transmission path. 3.The device according to claim 2, wherein the reception impedancematching circuit is further configured to match, based on a common modereflection parameter of a common mode reception path, an impedance of acommon mode input port to an impedance of the common mode receptionpath.
 4. The device according to claim 1, further comprising: anamplifier configured to amplify a power of at least one of the signalsprior to transmission with an amplification factor, wherein theamplification factor for the signals is based on the at least onereflection parameter.
 5. The device according to claim 1, wherein thefirst and second power line transmission paths are within a same powerline connected to the device.
 6. The device according to claim 1,wherein the first impedance is a conjugate complex impedance of thefirst power line transmission path, and the second impedance is aconjugate complex impedance of the second power line transmission path.7. The device according to claim 1, wherein the transmission impedancematching circuit is configured to individually match each transmissionfrequency.
 8. A device for power line communication, the devicecomprising: a multiple-input-multiple-output (MIMO) receiver configuredto concurrently receive signals via a first input port coupled to afirst power line reception path and a second input port coupled to asecond power line reception path, the first and second power linereception paths included in a plurality of power line reception paths ofa power line network; and a reception impedance matching circuitconfigured to identically match, based on at least one reflectionparameter of at least one of the first and second power line receptionpaths, a first input impedance of the first input port to a firstimpedance of the first power line reception path and a second inputimpedance of the second input port to a second impedance of the secondpower line reception path, wherein the at least one reflection parameteris predetermined.
 9. The device according to claim 8, wherein thereception impedance matching circuit is further configured to match,based on a common mode reflection parameter of a common mode receptionpath, an input impedance of a common mode input port to an impedance ofthe common mode reception path.
 10. The device according to claim 8,wherein the first and second power line reception paths are within asame power line connected to the device.
 11. The device according toclaim 8, wherein the first impedance is a conjugate complex impedance ofthe first power line reception path, and the second impedance is aconjugate complex impedance of the second power line reception path. 12.The device according to claim 8, wherein the reception impedancematching circuit is configured to individually match each receptionfrequency.
 13. A multiple-input-multiple-output (MIMO) method,comprising: concurrently transmitting, by a MIMO transmitter of adevice, signals via a first output port coupled to a first power linetransmission path and a second output port coupled to a second powerline transmission path, the first and second power line transmissionpaths included in a plurality of transmission paths of a power linenetwork; and identically matching, by a transmission impedance matchingcircuit of the device based on at least one reflection parameter of atleast one of the first and second power line transmission paths, a firstoutput impedance of the first output port to a first impedance of thefirst power line transmission path and a second output impedance of thesecond output port to a second impedance of the second power linetransmission path, wherein the at least one reflection parameter ispredetermined.
 14. The MIMO method according to claim 13, wherein thefirst and second power line transmission paths are within a same powerline connected to the device.
 15. The MIMO method according to claim 13,further comprising: concurrently receiving signals via a first inputport coupled to the first power line transmission path and a secondinput port coupled to the second power line transmission path; andmatching, based on the at least one reflection parameter, a first inputimpedance of the first input port to the first impedance of the firstpower line transmission path and a second input impedance of the secondinput port to the second impedance of the second power line transmissionpath.
 16. The MIMO method according to claim 15, further comprising:determining a common mode reflection parameter of a common modereception path, and matching, based on the common mode reflectionparameter, an impedance of a common mode input port to an impedance ofthe common mode reception path.
 17. The MIMO method according to claim13, wherein the transmission impedance matching circuit individuallymatches each transmission frequency in the identically matching.